More hover label style customizations

[chriddyp]

I'm working on Dash Themes and I'd like to customize the look and feel of the hover labels more. In order of importance:
1 - Customize the background and text color of the trace name. Currently the background is semi-transparent and the text color is dark, rendering the name of the trace illegible.


2 - Customize border color and width
3 - Generic CSS? For example, it'd be nice if I could experiment with box-shadow like https://bl.ocks.org/sarubenfeld/56dc691df199b4055d90e66b9d5fc0d2 in the same style as my theme's buttons:

[brianstamper]

Possibly related, allow control over hover text alignment independent of hover placement position left/right/center, as mentioned here #260 and here https://stackoverflow.com/questions/50003531/r-plotly-hover-label-text-alignment

[etpinard]

In brief, we should add attributes:

• hoverlabel.namecolor
• hoverlabel.bgnamecolor
• hoverlabel.borderwidth (hoverlabel.bordercolor is already a thing)

[etpinard]

and let's merge in #1665

• hoverlabel.opacity

[kristianmandrup]

Could you please add hoverlabel.nameborderwidth as well :)

[Braintelligence]

@etpinard The PR #3048 didn't include a namecolor setting, right? I'm currently running into problems with the readability of the name portion of a hoverlabel when the traces have a bright marker color (like yellow). I wish I could set the namecolor =(...

EDIT: Also super problems with one plot where I use a transparent marker color but black text color for the hoverlabel that doesn't get transported over to the name.

[antoinerg]

@chriddyp suggested supporting generic CSS. That would cover all possible styling option of CSS available now and in the future. Something like hoverlabel.style or hoverlabel.css ? What do you think?

[alexcjohnson]

supporting generic CSS

Sure, we support this already in our pseudo-HTML - ie <span style="...">styled text</span> so there's precedent for it. I suspect there will be easy ways to use this to break our fragile sizing and positioning system, but you'll know pretty quickly if that has happened 😅 And I'm sure people would find used for it!